The present invention relates generally to thermoplastic polymers having polymeric reinforcing phases dispersed therein.
In the past several decades, the use of polymers has transformed the world. Polymer science has rapidly evolved to make thousands of different thermoplastic and thermosetting products within the four corners of polymer physics: thermoplastic plastics, thermoplastic elastomers, thermoset plastics, and thermoset elastomers.
No large scale production of any polymer can rest on current ingredients or processing conditions. Reduction of cost, improvement of productivity, delivery of better performing, lower cost products all drive the polymer science industry. The situation is no different for thermoplastic compositions.
When formulating thermoplastic compositions for use in elevated temperature environments, other considerations become a further driving force. Generally, as the temperature of a composition increases during use, the flexural modulus of that composition decreases. Depending on the anticipated use of the composition, a decrease in flexural modulus may be undesirable and compromise performance of the composition in the intended application. While articles can be designed with a higher stiffness than the underlying composition inherently provides, design alone is not always able to compensate for a composition's relatively low flexural modulus in certain applications, particularly elevated temperature applications.
In order to alleviate this disadvantage, reinforcing fillers can be added to a composition to increase its flexural modulus. Fillers in general are often utilized for improving certain performance properties of compositions. Those properties are many and varied, ranging from impact strength to flame retardancy to name a few.
Known reinforcing fillers include both organic and inorganic materials. It is often the case that, whatever their type, fillers are formed prior to their addition to a composition. That is, they are formed ex-situ.
While the addition of conventional fillers to a composition in this manner has its benefits, it also has its shortcomings. Notably, addition of polymerized fillers for improving elevated temperature flexural modulus of a composition tends to make processing of the composition (e.g., into the shape of a desired article) more difficult. Those types of fillers generally increase the composition's viscosity and sometimes even require heating to relatively high temperatures in order to melt the polymerized filler effectively and/or disperse the polymerized filler throughout a composition during processing of, for example, neat compositions.
When incorporation of amorphous polymeric reinforcing filler is desired, these processing difficulties and efficiencies are even more prevalent. Effective dispersion of amorphous polymeric reinforcing filler often requires heating the composition to a temperature of at least about 100° C. greater than the glass transition temperature (Tg) of the amorphous polymeric reinforcing filler, which would typically already have a relatively high Tg.
When crystalline reinforcement is desired, processing temperatures of about 10° C. to about 30° C. greater than the melting temperature (Tm) of the polymerized reinforcing filler are generally required to effectively disperse that type of filler within a system. Melting temperatures of materials are generally much higher than glass transition temperatures. Thus, again this need for elevated temperatures can pose processing difficulties and efficiencies.
Increasing the viscosity of a composition by and large generally decreases the efficiency of processing of the composition due to excessive shear during heating. Further, the use of higher processing temperatures may lead to degradation of one or more of the other components in the composition being processed. Thus, when processing materials (e.g., thermoplastics) at elevated temperatures (e.g., when melt-processing such as for injection molding or calendering of the composition), it is generally desirable to decrease the viscosity of the compositions in order to increase production efficiency thereof and avoid the necessary use of higher temperatures.
Oils and similar processing aids have been utilized for this purpose with certain materials and in certain applications. The addition of those types of components, however, tends to increase the overall softness and flexibility of the resulting products, which may be undesirable for certain applications. Further, when liquid plasticizers are used to reduce a composition's viscosity during processing, those plasticizers can migrate undesirably within or out of the resulting composition and articles. Not only does this pose environmental concerns, but it also compromises intended performance properties of the composition and the article.